ELECTROLESS Ni-Fe ALLOY PLATING SOLUTION

ABSTRACT

An object of the present invention is to provide an electroless Ni—Fe alloy plating solution with which continuous plating can be carried out in a stable manner. An electroless Ni—Fe alloy plating solution comprising a nickel ion source, an iron ion source, a complexing agent and a reducing agent, wherein the iron ion source is a ferric ion source is provided. It is preferable that the ferric ion source is one or two or more iron salts selected from the group consisting of iron (III) sulfate, iron (III) chloride, iron alum, iron (III) oxide and iron (III) hydroxide. It is preferable that the content of the ferric ion is 0.001 to 1.0 mol/L at the time of the initial make-up of plating bath. It is preferable that the content of the ferrous ion is 0.1 mol/L or less at the time of the initial make-up of plating bath.

TECHNICAL FIELD

The present invention relates to an electroless Ni—Fe alloy plating solution.

BACKGROUND ART

Ni—Fe alloys containing 35 to 80% by mass of Ni (what is called permalloy) have high magnetic permeability and thus are used for applications such as magnetic field shielding materials, magnetic heads and wound magnetic cores. Of them, Ni—Fe alloys containing about 20% by mass of Fe are called PC permalloy and known as an excellent magnetic field shielding material having the highest magnetic permeability among the Ni—Fe alloys. Known methods for producing Ni—Fe alloy coating include rolling, sputtering, electroplating and electroless plating. Electroless plating is advantageous in that it is inexpensive, provides coating having uniform film thickness and excellent corrosion resistance and abrasion resistance, and can form coating on the surface of various types of materials.

Conventionally, electroless Ni—Fe alloy plating solutions containing a nickel ion source, an iron ion source, a complexing agent and a reducing agent have been known as an electroless Ni—Fe alloy plating solution used for electroless plating. For example, Patent Literature 1 discloses an electroless Ni—Fe alloy plating solution containing any of nickel sulfamate, nickel chloride and nickel sulfate as a nickel ion source, any of iron sulfamate, iron chloride and iron sulfate as an iron ion source and any of glycine, tartaric acid, malic acid, citric acid, ammonium tartrate, ammonium citrate, ammonium acetate and acetic acid as a complexing agent and any of dimethylaminoborane, morpholineborane, glyoxylic acid and ammonium hypophosphite as a reducing agent. Furthermore, Patent Literatures 2 and 3 and Non-patent literature 1 disclose an electroless Ni—Fe alloy plating solution using sodium hypophosphite as a reducing agent.

The iron ion sources in the electroless Ni—Fe alloy plating solutions disclosed in Patent Literatures 1 to 3 and Non-patent literature 1 are all a ferrous ion source which provides ferrous ions (divalent iron ions, Fe²⁺). Thus, these electroless Ni—Fe alloy plating solutions contain a nickel complex and a ferrous (II) complex at the time of the initial make-up of plating bath.

Herein, a nickel complex and free nickel ions which do not form a complex are referred to as a “nickel ion” without distinction unless otherwise required. Likewise, a ferrous (II) complex and free divalent iron ions which do not form a complex are referred to as a “ferrous ion” without distinction, and a ferric (III) complex and free trivalent iron ions which do not form a complex are referred to as a “ferric ion” without distinction.

CITATION LIST Patent Literature

Patent Literature 1: Japanese Patent Application; Japanese Translation of PCT International Application Publication No. 2007-512430

Patent Literature 2: Japanese Patent Application; Japanese Patent Laid-Open No. 2010-59512

Patent Literature 3: Japanese Patent Application; Japanese Patent Laid-Open No. H07-66034

Non Patent Literature

Non Patent Literature 1: Takiguchi Masanori, “Applications of electroless permalloy plating for EMI shielding,” Journal of the Surface Finishing Society of Japan, the Surface Finishing Society of Japan, Oct. 30, 2009, Volume 40, Issue 1, pp. 40-41

SUMMARY OF INVENTION Technical Problem

However, the electroless Ni—Fe alloy plating solutions disclosed in Patent Literatures 1 to 3 and Non-patent literature 1 have the disadvantage of difficulty in continuous plating. Thus, an object of the present invention is to provide an electroless Ni—Fe alloy plating solution with which continuous plating can be carried out in a stable manner.

Solution to Problem

The present inventors have conducted intensive studies on the disadvantage of difficulty in continuous plating with conventional electroless Ni—Fe alloy plating solutions, and have arrived at the following invention.

Thus, the electroless Ni—Fe alloy plating solution of the present invention is an electroless Ni—Fe alloy plating solution comprising a nickel ion source, an iron ion source, a complexing agent and a reducing agent, wherein the iron ion source is a ferric ion source.

It is preferable that in the electroless Ni—Fe alloy plating solution of the present invention, the ferric ion source be one or two or more iron salts selected from the group consisting of iron (III) sulfate, iron (III) chloride, iron alum, iron (III) oxide and iron (III) hydroxide.

It is preferable that in the electroless Ni—Fe alloy plating solution of the present invention, the content of the ferric ion be 0.001 to 1.0 mol/L at the time of the initial make-up of plating bath.

It is preferable that in the electroless Ni—Fe alloy plating solution of the present invention, the content of the ferrous ion be 0.1 mol/L or less at the time of the initial make-up of plating bath.

It is preferable that in the electroless Ni—Fe alloy plating solution of the present invention, the nickel ion source be one or two or more nickel salts selected from the group consisting of nickel chloride, nickel sulfate, nickel sulfamate, nickel hypophosphite, nickel citrate, nickel carbonate and nickel acetate.

It is preferable that in the electroless Ni—Fe alloy plating solution of the present invention, the complexing agent be one or two or more complexing agents selected from the group consisting of tartaric acid, citric acid, gluconic acid, pyrophosphoric acid, etidronic acid, alanine, glycine, glutamic acid, hydantoin, arginine, acetic acid, succinic acid, ascorbic acid, butyric acid, fumaric acid, pyruvic acid, lactic acid, malic acid, oxalic acid, ammonia, monoethanolamine, triethylenetetramine, triethanolamine, ethylenediamine, ethylenediaminetetraacetic acid and a salt thereof.

It is preferable that in the electroless Ni—Fe alloy plating solution of the present invention, the reducing agent be one or two or more reducing agents selected from the group consisting of hypophosphorous acid, hypophosphite, dimethylamineborane, titanium (III) and hydrazine.

Advantageous Effect of Invention

The electroless Ni—Fe alloy plating solution of the present invention contains a nickel complex and a ferric (III) complex at the time of the initial make-up of plating bath. Part of the ferric ions in the electroless Ni—Fe alloy plating solution sometimes change to a ferrous ion. The ferrous ion does not inhibit the deposition reaction of Ni—Fe alloy from nickel ions and ferric ions. Thus, with the electroless Ni—Fe alloy plating solution, reduction of the deposition rate of Ni-Fe alloy can be suppressed even when the amount of ferrous ions is increased when continuous plating is performed. In other words, continuous plating can be performed in a stable manner when the electroless Ni—Fe alloy plating solution is used.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a graph showing the relation among the number of times of plating, the deposition rate and the content of Fe in coating when continuous plating is performed using a conventional electroless Ni—Fe alloy plating solution.

FIG. 2 is a graph showing the relation between the time of blowing air and the concentration of ferrous ions when air is blown into a conventional electroless Ni—Fe alloy plating solution.

FIG. 3 is a graph showing the relation among the concentration of ferric ions, the deposition rate and the content of Fe in coating in a conventional electroless Ni—Fe alloy plating solution.

FIG. 4 is a graph showing the relation among the number of times of plating, the deposition rate and the content of Fe in coating when continuous plating is performed using the electroless Ni—Fe alloy plating solution of Example 1a.

FIG. 5 is a graph showing the relation among the concentration of ferrous ions, the deposition rate and the content of Fe in coating in the electroless Ni—Fe alloy plating solutions of Examples 2a to 2e.

DESCRIPTION OF EMBODIMENTS 1. Technical Idea Adopted in the Present Invention

To facilitate understanding of the invention of the present application, the problem with conventional electroless Ni—Fe alloy plating solutions containing a nickel ion source and a ferrous ion source as an iron ion source will be described. A plating solution having the composition shown in Table 1 was prepared as a conventional electroless Ni—Fe alloy plating solution (referred to as “Comparative Example 1”). In the Example, ferrous ammonium sulfate was used as the ferrous ion source.

TABLE 1 Comparative Example 1 Component Nickel ion NiSO₄ (mol/L) 0.06 constituting source plating bath Ferrous ion (NH₄)₂ Fe(SO₄)₂ 0.06 source (mol/L) Complexing Rochelle salt 0.23 agent (mol/L) Reducing Sodium 0.13 agent hypophosphite (mol/L) pH buffer Sodium 0.05 tetraborate (mol/L) Stabilizer Bismuth (ppm) 10 pH adjuster Ammonia water As needed Plating conditions pH 10.5 Bath temperature 70 (° C.)

Next, continuous plating was performed using the above electroless Ni—Fe alloy plating solution. More specifically, the continuous plating was performed as follows. First, a plating process was previously performed using the electroless Ni—Fe alloy plating solution for 30 minutes, and the concentration of the nickel ion, the ferrous ion and sodium hypophosphite, and the pH were measured before and after the plating process. Then, the amount of the components constituting the plating bath consumed per plating process was calculated. Subsequently, a procedure was repeated, including performing an actual plating process for 30 minutes, replenishing the components constituting the plating bath in an amount corresponding to the above amount consumed and performing a plating process again. The bath volume was 1 L, and the bath load was 1 dm²/L.

Then, the film thickness of the coating obtained by the respective plating processes was measured, and the composition of the coating was analyzed. The results are shown in FIG. 1 (a graph showing the relation among the “number of times of plating”, the “deposition rate” and the “content of Fe in the coating”). The horizontal axis of FIG. 1 shows the number of times of plating, the left vertical axis shows the deposition rate, and the right vertical axis shows the content of Fe in the coating. The content of Fe in the coating is the total amount of Fe detected in the coating. The form of Fe in the coating is not distinguished.

As shown in FIG. 1, no deposition reaction occurred in the second plating process. This provides the understanding that with the conventional electroless Ni—Fe alloy plating solution, the initial deposition rate could not be recovered and even the deposition reaction stopped in the second plating process even though the components constituting the plating bath consumed in the first plating process were replenished. This shows that performing continuous plating is difficult with the conventional electroless Ni—Fe alloy plating solution. Furthermore, the deposition reaction stopped in the second plating process presumably because the composition of the plating bath was significantly changed.

Furthermore, the results of intensive studies are that the presence of ferric ions in the conventional electroless Ni—Fe alloy plating solution inhibits the deposition reaction. The grounds will be described with reference to FIG. 2 and FIG. 3.

First, air was blown into the above electroless Ni-Fe alloy plating solution at a rate of 1 L/ minute, and the change of the concentration of ferrous ions in the electroless Ni—Fe alloy plating solution was measured. The results are shown in FIG. 2 (a graph showing the relation between the “time of blowing air” and the “concentration of ferrous ions (Fe²⁺)”). FIG. 2 shows that as the time of blowing air becomes longer, the concentration of the ferrous ion in the electroless Ni—Fe alloy plating solution decreases. This suggests that part of the ferrous ions is changed to ferric ions due to dissolved oxygen.

Next, a solution was prepared by adding iron (III) chloride to the above electroless Ni—Fe alloy plating solution as a ferric ion (referred to as “Comparative Example 2”), and the deposition rate when plating process was performed using the solution was measured. The results are shown in FIG. 3 (a graph showing the relation between the “concentration of ferric ions (Fe³⁺) in the electroless Ni—Fe alloy plating solution” and the “deposition rate”). FIG. 3 shows that as the amount of ferric ions in the electroless Ni—Fe alloy plating solution becomes larger, the deposition rate significantly decreases. In other words, the results suggest that ferric ions in the electroless Ni—Fe alloy plating solution inhibited the deposition reaction of Ni-Fe alloy from nickel ions and ferrous ions.

The above results suggest the following. That is, the concentration of ferrous ions in a conventional electroless Ni—Fe alloy plating solution containing a nickel ion source and a ferrous ion source is reduced due to change of ferrous ions into ferric ions. Furthermore, these ferric ions inhibit the deposition reaction of Ni-Fe alloy from nickel ions and ferrous ions. Thus, with the conventional electroless Ni—Fe alloy plating solution containing a nickel ion source and a ferrous ion source, continuous plating cannot be performed in a stable manner even if continuous plating is performed while replenishing components constituting a plating bath consumed in a plating process.

The present inventors conducted further intensive studies and as a result have arrived at using ferric ions (Fe³⁺) instead of ferrous ions (Fe²⁺) in the deposition reaction of Ni—Fe alloy. The inventors then found that continuous plating can be performed in a stable manner using an electroless Ni—Fe alloy plating solution containing a nickel ion source and a ferric ion source. Based on this technical idea, the inventors have arrived at the present invention described below.

2. Embodiments of Electroless Ni—Fe Alloy Plating Solution of the Present Application 2-1. Components Constituting Electroless Ni—Fe Alloy Plating Solution

The electroless Ni—Fe alloy plating solution of the present embodiment comprises a nickel ion source, an iron ion source, a complexing agent and a reducing agent, wherein the iron ion source is a ferric ion source, and nickel ions and ferric ions are used for the deposition reaction of a Ni—Fe alloy. When the electroless Ni—Fe alloy plating solution is used, a Ni—Fe alloy coating in which the content of Ni is 65 to 99% by mass and the content of Fe is 1 to 35% by mass can be obtained.

(1) Nickel Ion Source

The electroless Ni—Fe alloy plating solution of the present invention contains a nickel ion source. Nickel ions supplied from the nickel ion source occurs mainly as a nickel complex in the electroless Ni—Fe alloy plating solution. Examples of the nickel ion source include one or two or more nickel salts selected from the group consisting of nickel chloride, nickel sulfate, nickel sulfamate, nickel hypophosphite, nickel citrate, nickel carbonate and nickel acetate. Nickel sulfate and nickel chloride are particularly preferred as the nickel ion source because they are highly soluble and provides stable deposition rates.

The electroless Ni—Fe alloy plating solution contains the nickel ion source at preferably 0.001 to 1.0 mol/L, and more preferably 0.001 to 0.1 mol/L in terms of nickel. A content of the nickel ion source of less than 0.001 mol/L at the time of the initial make-up of plating bath is not preferred because the deposition rate of Ni-Fe alloy coating may excessively decrease. By contrast, a content of the nickel ion source of more than 0.1 mol/L is not preferred because the content of Fe in the coating becomes lower than that in the intended composition and a coating having good surface properties cannot be obtained.

(2) Ferric Ion Source

The electroless Ni—Fe alloy plating solution of the present invention comprises a ferric ion source as an iron ion source. The ferric ion source supplies ferric ions (trivalent iron ion, Fe³⁺), and is different from the ferrous ion source which has been used in conventional electroless Ni—Fe alloy plating solutions. The ferric ion supplied from the ferric ion source occurs mainly as a ferric (III) complex in the electroless Ni—Fe alloy plating solution. Examples of the ferric ion source include one or two or more iron salts selected from the group consisting of iron (III) sulfate, iron (III) chloride, iron alum, iron (III) oxide and iron (III) hydroxide. Iron (III) sulfate and iron (III) chloride are particularly preferred as the ferric ion source because they are highly soluble in plating bath and provide stable deposition rates.

The electroless Ni—Fe alloy plating solution contains the ferrous ion source at preferably 0.001 to 1.0 mol/L, and more preferably 0.001 to 0.1 mol/L in terms of iron. A content of the ferric ion source of less than 0.001 mol/L at the time of the initial make-up of plating bath is not preferred because a Ni—Fe alloy coating in which the content of Fe is 1 to 35% by mass cannot be obtained, or because the deposition rate of Ni-Fe alloy coating may excessively decrease. By contrast, a content of the ferric ion source of more than 0.1 mol/L is not preferred because deposition reaction may be inhibited and no coating may be formed.

The ferric ion in the electroless Ni—Fe alloy plating solution is reduced by the action of the reducing agent described later, and part of the ferric ions is changed to ferrous ions. However, it is preferable that the content of the ferrous ion in the electroless Ni—Fe alloy plating solution at the time of the initial make-up of plating bath be 0.1 mol/L or less. A content of the ferrous ion at the time of the initial make-up of plating bath of more than 0.1 mol/ L is not preferred because the deposition reaction of Ni—Fe alloy from nickel ions and ferric ions may be inhibited.

(3) Complexing Agent

The electroless Ni—Fe alloy plating solution of the present invention contains, as a complexing agent, one or two or more selected from the group consisting of tartaric acid, citric acid, gluconic acid, pyrophosphoric acid, etidronic acid (1-hydroxyethane-1,1-diphosphonic acid, sodium salt, HEDP), alanine, glycine, glutamic acid, hydantoin, arginine, acetic acid, succinic acid, ascorbic acid, butyric acid, fumaric acid, pyruvic acid, lactic acid, malic acid, oxalic acid, ammonia, monoethanolamine, triethylenetetramine, triethanolamine, ethylenediamine (EDA), ethylenediaminetetraacetic acid (EDTA) and a salt thereof. It is preferable that two or more complexing agents be used from the viewpoint of formation of a more stable complex and suppression of precipitation. Examples of the salts of ethylenediaminetetraacetic acid include tetraammonium ethylenediaminetetraacetate.

It is preferable to select and use a complexing agent capable of forming a stable complex with a nickel ion and a ferric ion. It is preferable to use one or more selected from the group consisting of alanine, glycine, glutamic acid, hydantoin, arginine, ethylenediamine, ethylenediaminetetraacetic acid and ethylenediaminetetraacetate as a first complexing agent suitable for forming a nickel complex. The first complexing agent is coordinated with a nickel ion and can form a stable nickel complex. By contrast, it is preferable to use one or more selected from the group consisting of Rochelle salt, trisodium citrate, sodium gluconate, potassium pyrophosphate, etidronic acid, lactic acid, malic acid, acetic acid and oxalic acid as a second complexing agent suitable for forming a ferric (III) complex. The second complexing agent is coordinated with a ferric ion and can form a stable ferric (III) complex. A combination using alanine as the first complexing agent and Rochelle salt as the second complexing agent, and a combination using ammonia as the first complexing agent and citric acid and/or Rochelle salt as the second complexing agent are particularly preferred from the viewpoint of, for example, bath stability, suitable deposition rates and stability of content of Fe in coating. One of the first complexing agents and one of the second complexing agents may be used, respectively, and two or more of them may be used, and the latter case provides an effect of, for example, preventing precipitation.

The preferred content of the complexing agent in the electroless Ni—Fe alloy plating solution at the time of the initial make-up of plating bath is related to not only the type of complexing agents but also the content of the nickel ion source and the ferric ion source. For example, when nickel sulfate or nickel chloride is used as the nickel ion source and its content is 0.06 mol/L in terms of nickel, and iron (III) sulfate is used as the ferric ion source and its content is 0.02 mol/L in terms of iron, and alanine is used as the first complexing agent and Rochelle salt is used as the second complexing agent, or ammonia is used as the first complexing agent and citric acid and/or Rochelle salt is used as the second complexing agent, the content of the first complexing agent is preferably 0.04 to 0.5 mol/L, and the content of the second complexing agent is preferably 0.12 to 0.5 mol/L. A content of the respective complexing agents of less than the lower limit of the above range is not preferred because formation of a complex is insufficient, and nickel or iron is likely to be precipitated. By contrast, a content of the respective complexing agents of more than the upper limit of the above range is not preferred because not only a significant effect cannot be obtained but also the resource is wasted.

(4) Reducing Agent

The electroless Ni—Fe alloy plating solution of the present invention contains one or two or more selected from the group consisting of hypophosphorous acid, hypophosphite, dimethylamineborane, titanium (III) and hydrazine as a reducing agent. Examples of the hypophosphites include sodium hypophosphite, potassium hypophosphite and ammonium hypophosphite. Sodium hypophosphite is particularly preferred as the reducing agent because little autolysis occurs and thus controlling its concentration is easy. When sodium hypophosphite is used as a reducing agent, a Ni—Fe alloy containing phosphorus derived from sodium hypophosphite (Ni—Fe—P alloy) is deposited.

The preferred content of the reducing agent in the electroless Ni—Fe alloy plating solution at the time of the initial make-up of plating bath is related to not only the type of complexing agents but also the content of the nickel ion and the ferric ion. For example, when nickel sulfate is used as the nickel ion source and its content is 0.06 mol/L in terms of nickel, and iron (III) sulfate is used as the ferric ion source and its content is 0.02 mol/L in terms of iron, and sodium hypophosphite is used as the reducing agent, the content of sodium hypophosphite is preferably 0.05 to 0.5 mol/L. A content of sodium hypophosphite of less than 0.05 mol/L is not preferred because sufficient reducing action cannot be obtained, and thus the deposition rate becomes extremely low, or deposition may not occur. By contrast, a content of sodium hypophosphite of more than 0.5 mol/L is not preferred because decomposition of the bath may occur.

(5) Other Constituent Components

The electroless Ni—Fe alloy plating solution of the present invention may contain a pH adjuster, a pH buffer, a stabilizer and the like in addition to the above components.

pH adjuster: ammonia, ammonium hydroxide, sodium hydroxide, potassium hydroxide, tetramethylammonium hydroxide and the like may be used as a pH adjuster for the electroless Ni—Fe alloy plating solution of the present invention.

pH buffer: sodium tetraborate, sodium carbonate, boric acid and the like may be used as a pH buffer for the electroless Ni—Fe alloy plating solution of the present invention.

Stabilizer: bismuth, lead, antimony, vanadium, thiourea, sodium thiocyanate, sodium nitrobenzenesulfonate (MBS) and 2-propyn-1-ol and the like may be used as a stabilizer for the electroless Ni-Fe alloy plating solution of the present invention.

2-2. Method for Preparing Plating Solution

The electroless Ni—Fe alloy plating solution of the present invention can be prepared by adding the components described above to water and mixing them by stirring. For a nickel complex and a ferric (III) complex to be present in the electroless Ni—Fe alloy plating solution in a stable manner, it is preferable to form a stable nickel complex and a stable ferric (III) complex previously. To this end, it is preferable to add a complexing agent to pure water first, and for example, the first complexing agent, the second complexing agent, a nickel ion source and a ferric ion source are added to pure water, and then a pH buffer, a reducing agent, a stabilizer, a pH adjuster and the like are added.

It is preferable that the pH of the electroless Ni-Fe alloy plating solution be adjusted to pH 6 to 13 by adding a pH adjuster when a sulfuric acid bath is used. A pH of less than 6 is not preferred because the deposition rate becomes extremely low or deposition may not occur. By contrast, a pH of more than 13 is not preferred because decomposition of the bath may occur.

2-3. Conditions of Plating

Bath temperature: the bath temperature for the electroless Ni—Fe alloy plating solution of the present invention in the plating process is preferably 25° C. or higher, more preferably 40 to 100° C. A bath temperature of lower than 40° C. is not preferred because the deposition rate becomes extremely low or deposition may not occur. By contrast, a bath temperature of higher than 100° C. is not preferred because the deposition rate becomes extremely high, control of film thickness of coating is difficult, and thus a coating having good surface properties cannot be obtained.

Deposition rate: a coating can be formed at a deposition rate of 0.1 to 30 μm/ hour with the electroless Ni—Fe alloy plating solution of the present invention by adjusting the pH and the bath temperature. A deposition rate of less than 0.1 μm/ hour is not preferred because the time of immersion needs to be extended in order to obtain a coating having a desired film thickness, and thus industrial productivity cannot be achieved. By contrast, a deposition rate of more than 30 μm/ hour is not preferred because a coating having good surface properties cannot be obtained, and decomposition of the bath is likely to occur. The deposition rate can be mainly controlled by concentrations of metals, bath temperature and pH.

2-4. Method of Plating

The method of plating using the electroless Ni—Fe alloy plating solution of the present embodiment is performed by dipping objects in the electroless Ni—Fe alloy plating solution. The object to be plated is not particularly limited as long as the catalytic treatment described later can be done. For example, a conductor such as metal, and a non-conductor such as resin and glass may be used. Furthermore, an object having any shape, such as plate, film and a molded article may be adopted as the object to be plated. A coating made of Ni—Fe alloy can be formed on the surface of the object to be plated by the plating method. The composition of the resulting coating includes, for example, 65 to 95% by mass of Ni and 1 to 35% by mass of Fe. When sodium hypophosphite is used as a reducing agent, a coating made of a Ni—Fe alloy containing 0.1 to 7% by mass of P may be formed.

A coating made of Ni—Fe coating formed using the electroless Ni—Fe alloy plating solution of the present embodiment has high magnetic permeability and is suitable for applications such as magnetic field shielding materials, magnetic heads and wound magnetic cores.

The electroless Ni—Fe alloy plating solution of the present embodiment contains a nickel complex and a ferric (III) complex at the time of the initial make-up of plating bath. Part of the ferric ions is changed to ferrous ions by the action of the reducing agent as deposition reaction proceeds, or with time. The ferrous ion does not inhibit the deposition reaction of Ni—Fe alloy from nickel ions and ferric ions. Thus, with the electroless Ni—Fe alloy plating solution, reduction of the deposition rate can be suppressed even when the amount of ferrous ions increases when continuous plating is performed while replenishing components constituting a plating bath consumed in a plating process. In other words, the electroless Ni—Fe alloy plating solution enables continuous plating to be performed in a stable manner and makes continuous operation possible.

The components constituting a plating bath consumed may be replenished every time a plating process is performed or after several plating processes.

The embodiments of the present invention described above are a mode of the present invention, and obviously they can be appropriately modified without departing from the spirit of the present invention. Hereinafter the present invention will be described in more detail with reference to Examples, but the present invention is not limited to the following Examples.

EXAMPLES 1. Evaluation of Continuous Plating

First, the electroless Ni—Fe alloy plating solution of Example 1a shown in Table 2 was prepared. The plating solution was prepared by adding the first complexing agent, the second complexing agent, a nickel ion source and a ferric ion source to pure water in that order, and then adding other agents such as a reducing agent and mixing them. The electroless Ni—Fe alloy plating solution of Example 1a contains a nickel complex and a ferric (III) complex in a stable state at the time of the initial make-up of plating bath.

Next, a copper plate for Hull cell (registered trademark) made of rolled copper (made by YAMAMOTO-MS Co., Ltd.) was prepared as an object to be plated, and the object was pretreated. In the pretreatment, the object to be plated was degreased by dipping the object in an alkaline degreasing agent (made by Meltex Inc.) for 3 minutes and then acid activated by dipping in 10% sulfuric acid for 1 minute, and subsequently Pd catalyst was applied thereto by dipping in an ion-type Pd catalyzer (Act-440 made by Meltex Inc.) for 3 minutes.

Then the object to be plated which had been pretreated was subjected to continuous plating using the electroless Ni—Fe alloy plating solution of Example 1a. More specifically, a plating process was previously performed using the electroless Ni—Fe alloy plating solution for 30 minutes, and the concentrations of the nickel ion, the ferric ion and sodium hypophosphite and the pH were measured before and after the plating process. Then the amounts of the components constituting the plating bath consumed per plating process were calculated. Subsequently, a procedure was repeated, including performing an actual plating process for 30 minutes, replenishing the components constituting the plating bath in an amount corresponding to the above amount consumed and performing a plating process again. The bath volume was 1 L and the bath load was 1 dm²/L.

Then, the composition of the coating formed on the surface of the object plated by the respective plating processes was analyzed using Micro-XRF Spectrometer (M4 Tornado made by Bruker) in a quantitative analysis mode. In all the resulting coatings, the content of Ni was 65 to 95% by mass, the content of Fe was 1 to 35% by mass, and the content of P was 0.1 to 7% by mass. The deposition rate was calculated from the film thickness of the resulting coating. The results are shown in FIG. 4 (a graph showing the relation among the “number of times of plating”, the “deposition rate” and the “content of Fe in the coating.”) The horizontal axis of FIG. 4 shows the number of times of plating, the left vertical axis shows the deposition rate and the right vertical axis shows the content of Fe in the coating.

TABLE 2 Ex. 1a Component Nickel ion NiSO₄ (mol/L) 0.06 constituting source plating bath Ferric ion Fe₂ (SO₄)₃ 0.01 source (mol/L) First Alanine (mol/L) 0.1 complexing agent Second Rochelle salt 0.3 complexing (mol/L) agent Reducing Sodium 0.15 agent hypophosphite (mol/L) pH buffer Sodium 0.05 tetraborate (mol/L) Stabilizer 2-propyn-1-ol 10 (ppm) pH adjuster NaOH 0.01 Plating conditions pH 9.5 Bath temperature 70 (° C.)

FIG. 4 shows that with the electroless Ni—Fe alloy plating solution of Example 1a, the decrease in deposition rate and the decrease in the content of Fe in the coating did not occur even when the number of times of plating increased. This provides the understanding that when the above electroless Ni—Fe alloy plating solution of Example 1a is used, the original deposition rate can be recovered by replenishing the components constituting the plating bath consumed in a plating process, and that change of the composition of the plating bath is suppressed, and the composition of the bath is stable.

Furthermore, a comparison between FIG. 4 (Example 1a) and FIG. 1 (Comparative Example 1) reveals that continuous plating became possible when a ferric ion source was used as the iron ion source for the electroless Ni—Fe alloy plating solution instead of a ferrous ion source.

2. Evaluation of Influence of Ferrous Ion

Next, the electroless Ni—Fe alloy plating solution of Example 2a shown in Table 3 was prepared in the same manner as in Example la. Then 0.01 to 0.04 mol/L of FeSO₄ was added to the electroless Ni—Fe alloy plating solution of Example 2a as the ferrous ion source to prepare the electroless Ni—Fe alloy plating solutions of Examples 2b to 2e shown in Table 3. The same object to be plated as that used in Example 1a was dipped in the electroless Ni—Fe alloy plating solutions of Examples 2b to 2e for 30 minutes to perform a plating process.

The composition of the coating prepared using the electroless Ni—Fe alloy plating solution of Examples 2a to 2e was analyzed in the same manner as in Example 1a, and as a result, the content of Ni was 65 to 95% by mass, the content of Fe was 1 to 35% by mass, and the content of P was 0.1 to 7% by mass in all cases. Furthermore, the deposition rate was calculated in the same manner as in Example 1a. The results are shown in FIG. 5 (a graph showing the relation among the “concentration of the ferrous ion,” the “deposition rate” and the “content of Fe in the coating.”) The horizontal axis of FIG. 5 shows the concentration of Fe²⁺ added, i.e., the concentration of the ferrous ion source (FeSO₄) added, and the left vertical axis shows the deposition rate and the right vertical axis shows the content of Fe in the coating.

TABLE 3 Ex. 2a Ex. 2b Ex. 2c Ex. 2d Ex. 2e Component Nickel ion NiSO₄ (mol/L) 0.06 0.06 0.06 0.06 0.06 constituting source plating bath Ferric ion Fe₂ (SO₄)₃ 0.01 0.01 0.01 0.01 0.01 source (mol/L) First Alanine (mol/L) 0.1 0.1 0.1 0.1 0.1 complexing agent Second Rochelle salt 0.3 0.3 0.3 0.3 0.3 complexing (mol/L) agent Reducing Sodium 0.15 0.15 0.15 0.15 0.15 agent hypophosphite (mol/L) pH buffer Sodium 0.05 0.05 0.05 0.05 0.05 tetraborate (mol/L) Stabilizer 2-propyn-1-ol 10 10 10 10 10 (ppm) pH adjuster NaOH As As As As As needed needed needed needed needed Ferrous ion source FeSO₄ (mol/L) 0 0.01 0.02 0.03 0.04 Plating conditions pH 9.5 9.5 9.5 9.5 9.5 Bath temperature 70 70 70 70 70 (° C.)

As shown in Table 3, the electroless Ni—Fe alloy plating solution of Example 2a contains a nickel complex and a ferric (III) complex but no ferrous ions at the time of the initial make-up of plating bath. The electroless Ni—Fe alloy plating solutions of Examples 2b to 2e contain a nickel complex and a ferric (III) complex, and also 0.01 to 0.04 mol/L of ferrous ions at the time of the initial make-up of plating bath. The ferrous ion in the electroless Ni—Fe alloy plating solutions of Examples 2b to 2e is considered to occur mainly as a ferrous (II) complex. FIG. 5 shows that although the electroless Ni—Fe alloy plating solutions of Examples 2b to 2e contain a ferrous ion, the plating solutions provide a deposition rate and a content of Fe in the coating equivalent to those in the case of using the electroless Ni—Fe alloy plating solution of Example 2a which does not contain a ferrous ion. This suggests that the ferrous ion does not inhibit the deposition reaction of Ni—Fe alloy from nickel ions and ferric ions.

By contrast, FIG. 3 shows that in the case of using the electroless Ni—Fe alloy plating solution which contains a nickel complex and a ferrous (II) complex at the time of the initial make-up of plating bath and to which a ferric ion is added (corresponding to Comparative Example 2 described above), the deposition rate decreases as the amount of ferric ions is increased. This suggests that the ferric ion has inhibited the deposition reaction of Ni—Fe alloy from nickel ions and ferrous ions.

The above results show that when the electroless Ni-Fe alloy plating solution of Examples 2a to 2e containing the nickel complex and the ferric (III) complex at the time of the initial make-up of plating bath is used, inhibition of deposition reaction is suppressed and thus the composition of the bath is stable compared with the case where a conventional electroless Ni—Fe alloy plating solution containing a nickel complex and a ferrous (II) complex at the time of the initial make-up of plating bath is used. The results also show that good plating can be performed when the content of ferrous ions is 0.01 to 0.04 mol/L in the electroless Ni—Fe alloy plating solution containing a nickel complex and a ferric (III) complex.

Next, electroless Ni—Fe alloy plating solutions prepared by changing the type and the content of the components constituting the plating bath are evaluated.

3. Evaluation of Type of Metal Ion Source

First, the electroless Ni—Fe alloy plating solutions of Examples 3a and 3b shown in Table 4 were prepared in the same manner as in Example 2a and a plating process was performed. The electroless Ni—Fe alloy plating solutions of Examples 3a and 3b are the same except that the type of the nickel ion source and the type and concentration of the ferric ion source are different.

Then the composition of the coating prepared using the electroless Ni—Fe alloy plating solution of Examples 3a and 3b was analyzed in the same manner as in Example 2a, and as a result, the content of Ni was 65 to 95% by mass, the content of Fe was 1 to 35% by mass and the content of P was 0.1 to 7% by mass in all cases. Furthermore, the deposition rate was calculated in the same manner as in Example 2a and bath stability was visually evaluated. The results are shown in Table 4. Symbol “-” in tables (Tables 4 to 13) means that the corresponding component was not added. Symbol “⊚” means that bath stability is excellent without deposition on the object other than the object to be plated (e.g., the plating bath and stirrer) or precipitation after the completion of plating. Symbol “ο” means that bath stability is substantially good and plating have been performed well though deposition of alloy was found on the stirrer at the completion of plating.

TABLE 4 Ex. 3a Ex. 3b Component Nickel ion NiCl₂ (mol/L) 0.06 — constituting source NiSO₄ (mol/L) — 0.06 plating bath Ferric ion FeCl₃ (mol/L) 0.02 — source Fe₂ (SO₄)₃ — 0.06 (mol/L) First Alanine (mol/L) 0.1 0.1 complexing agent Second Sodium 0.3 0.3 complexing tartrate agent (mol/L) Reducing Sodium 0.15 0.15 agent hypophosphite (mol/L) pH buffer Sodium 0.05 0.05 tetraborate (mol/L) Stabilizer 2-propyn-1-ol 10 10 (ppm) pH adjuster NaOH As As needed needed Plating conditions pH 9.5 9.5 Bath temperature 70 70 (° C.) Deposition rate (μm/h) 5.7 6.3 Bath stability ⊚ ⊚

Table 4 shows that nickel chloride and nickel sulfate may be used as a nickel ion source, and iron (III) chloride and iron (III) sulfate may be used as a ferric ion source for the electroless Ni—Fe alloy plating solution. The table also shows that the electroless Ni-Fe alloy plating solutions of Examples 3a and 3b have excellent bath stability. Furthermore, since the electroless Ni—Fe alloy plating solutions of Examples 3a and 3b have excellent bath stability, continuous plating can be performed in a stable manner.

4. Evaluation of Concentration of Metal Ion Source

First, the electroless Ni—Fe alloy plating solutions of Examples 4a to 4d shown in Table 5 were prepared in the same manner as in Example 3a, and a plating process was performed. The electroless Ni—Fe alloy plating solutions of Examples 4a to 4d are the same except that the concentration of the ferric ion source, i.e., iron (III) sulfate is different.

Then the composition of the coating prepared using the electroless Ni—Fe alloy plating solution of Examples 4a to 4d was analyzed in the same manner as in Example 3a, and as a result, the content of Ni was 65 to 95% by mass, the content of Fe was 1 to 35% by mass, and the content of P was 0.1 to 7% by mass in all cases. Furthermore, the deposition rate was calculated and bath stability was evaluated in the same manner as in Example 3a. The results are shown in Table 5.

TABLE 5 Ex. 4a Ex. 4b Ex. 4c Ex. 4d Component Nickel ion NiSO₄ (mol/L) 0.06 0.06 0.06 0.06 constituting source plating bath Ferric ion Fe₂ (SO₄)₃ 0.006 0.009 0.01 0.012 source (mol/L) First Alanine (mol/L) 0.1 0.1 0.1 0.1 complexing agent Second Sodium 0.3 0.3 0.3 0.3 complexing tartrate agent (mol/L) Reducing Sodium 0.15 0.15 0.15 0.15 agent hypophosphite (mol/L) pH buffer Sodium 0.05 0.05 0.05 0.05 tetraborate (mol/L) Stabilizer 2-propyn-1-ol 10 10 10 10 (ppm) pH adjuster NaOH As As As As needed needed needed needed Plating conditions pH 10 10 10 10 Bath temperature 70 70 70 70 (° C.) Deposition rate (μm/h) 9.3 6.1 5.5 4.1 Bath stability ⊚ ⊚ ⊚ ⊚

Table 5 shows that a content of iron (III) sulfate of 0.006 to 0.012 mol/L in the electroless Ni—Fe alloy plating solutions provides excellent bath stability. This suggests that continuous plating can be performed in a stable manner with the electroless Ni—Fe alloy plating solutions of Examples 4a to 4d.

5. Evaluation of Type of Complexing Agent

First, the electroless Ni—Fe alloy plating solutions of Examples 5a to 5k shown in Table 6 were prepared in the same manner as in Example 3a and a plating process was performed. The electroless Ni—Fe alloy plating solutions of Examples 5a to 5k are the same except that the type of the complexing agent is different. For the electroless Ni—Fe alloy plating solutions of Examples 5a to 5d, any of trisodium citrate, sodium gluconate, potassium pyrophosphate and etidronic acid (1-hydroxyethane-1,1-diphosphonic acid, sodium salt, HEDP) was used alone as a complexing agent. These complexing agents act on both of the nickel ion and the ferric ion. In Table 6, the complexing agents used in Examples 5a to 5k are listed in the column of the second complexing agent.

By contrast, two complexing agents were used for the electroless Ni—Fe alloy plating solutions of Examples 5e to 5k. Any of alanine, glycine and glutamic acid was used for the electroless Ni—Fe alloy plating solutions of Examples 5e to 5g as the first complexing agent, and Rochelle salt was used as the second complexing agent. Furthermore, any of alanine, glycine, glutamic acid and taurine was used for the electroless Ni—Fe alloy plating solutions of Examples 5h to 5k as the first complexing agent, and sodium gluconate was used as the second complexing agent.

Then the composition of the coating prepared using the electroless Ni—Fe alloy plating solution of Examples 5a to 5k was analyzed in the same manner as in Example 3a, and as a result, the content of Ni was 65 to 95% by mass, the content of Fe was 1 to 35% by mass and the content of P was 0.1 to 7% by mass in all cases. Furthermore, the deposition rate was calculated and bath stability was evaluated in the same manner as in Example 3a. The results are shown in Table 6.

TABLE 6 Ex. 5a Ex. 5b Ex. 5c Ex. 5d Ex. 5e Ex. 5f Component Nickel ion NiSO₄ (mol/L) 0.06 0. 06 0.06 0.06 0.06 0.06 constituting source plating bath Ferric ion Fe₂ (SO₄)₃ 0.01 0.01 0.01 0.01 0.01 0.01 source (mol/L) First Alanine (mol/L) — — — — 0.1 — complexing Glycine (mol/L) — — — — — 0.1 agent Glutamic acid — — — — — — (mol/L) Taurine (mol/L) — — — — — — Second Rochelle salt — — — — 0.3 0.3 complexing (mol/L) agent Trisodium 0.3 — — — — — citrate (mol/L) Sodium — 0.3 — — — — Gluconate (mol/L) Potassium — — 0.3 — — — pyrophosphate (mol/L) HEDP (mol/L) — — — 0.3 — — Reducing Sodium 0.15 0.15 0.15 0.15 0.15 0.15 agent hypophosphite (mol/L) pH buffer Sodium 0.05 0.05 0.05 0.05 0.05 0.05 tetraborate (mol/L) Stabilizer 2-propyn-1-ol 10 10 10 10 10 10 (ppm) pH adjuster NaOH As As As As As As needed needed needed needed needed needed Plating conditions pH 9.5 9.5 9.5 9.5 9.5 9.5 Bath temperature 70° C. 70° C. 70° C. 70° C. 70° C. 70° C. (° C.) Deposition rate (μm/h) 0.2 1.7 3.5 0.4 6.3 4.4 Bath stability ⊚ ⊚ ⊚ ⊚ ⊚ ⊚ Ex. 5g Ex. 5h Ex. 5i Ex. 5j Ex. 5k Component Nickel ion NiSO₄ (mol/L) 0.06 0.06 0.06 0.06 0.06 constituting source plating bath Ferric ion Fe₂ (SO₄)₃ 0.01 0.01 0.01 0.01 0.01 source (mol/L) First Alanine (mol/L) — 0.1 — — — complexing Glycine (mol/L) — — 0.1 — — agent Glutamic acid 0.1 — — 0.1 — (mol/L) Taurine (mol/L) — — — — 0.1 Second Rochelle salt 0.3 — — — — complexing (mol/L) agent Trisodium — — — — — citrate (mol/L) Sodium — 0.3 0.3 0.3 0.3 Gluconate (mol/L) Potassium — — — — — pyrophosphate (mol/L) HEDP (mol/L) — — — — — Reducing Sodium 0.15 0.15 0.15 0.15 0.15 agent hypophosphite (mol/L) pH buffer Sodium 0.05 0.05 0.05 0.05 0.05 tetraborate (mol/L) Stabilizer 2-propyn-1-ol 10 10 10 10 10 (ppm) pH adjuster NaOH As As As As As needed needed needed needed needed Plating conditions pH 9.5 9.5 9.5 9.5 9.5 Bath temperature 70° C. 70° C. 70° C. 70° C. 70° C. (° C.) Deposition rate (μm/h) 1.9 3.6 2.9 0.9 1.7 Bath stability ⊚ ⊚ ⊚ ⊚ ⊚

Table 6 shows that the combination of complexing agents described in Table 6 can be used for the electroless Ni—Fe alloy plating solution and the combination provides excellent bath stability in all cases. This suggests that continuous plating can be performed in a stable manner with the electroless Ni—Fe alloy plating solutions of Examples 5a to 5k.

6. Evaluation of Concentration of Complexing Agent

First, the electroless Ni—Fe alloy plating solutions of Examples 6a to 6e shown in Table 7 were prepared in the same manner as in Example 3a. The electroless Ni—Fe alloy plating solutions of Examples 6a and 6b are the same except that the content of the first complexing agent is different, and the electroless Ni—Fe alloy plating solutions of Examples 6c to 6e are the same except that the content of the second complexing agent is different.

Then the composition of the coating prepared using the electroless Ni—Fe alloy plating solution of Examples 6a to 6e was analyzed in the same manner as in Example 3a, and as a result, the content of Ni was 65 to 95% by mass, the content of Fe was 1 to 35% by mass and the content of P was 0.1 to 7% by mass in all cases. Furthermore, the deposition rate was calculated and bath stability was evaluated in the same manner as in Example 3a. The results are shown in Table 7.

TABLE 7 Ex. 6a Ex. 6b Ex. 6c Ex. 6d Ex. 6e Component Nickel ion NiSO₄ (mol/L) 0.06 0.06 0.06 0.06 0.06 constituting source plating bath Ferric ion Fe₂ (SO₄)₃ 0.06 0.06 0.06 0.06 0.06 source (mol/L) First Alanine (mol/L) 0.05 0.15 0.1 0.1 0.1 complexing agent Second Sodium 0.3 0.3 0.1 0.2 0.4 complexing tartrate agent (mol/L) Reducing Sodium 0.15 0.15 0.15 0.15 0.15 agent hypophosphite (mol/L) pH buffer Sodium 0.05 0.05 0.05 0.05 0.05 tetraborate mol/L) Stabilizer 2-propyn-1-ol 10 10 10 10 10 (ppm) pH adjuster NaOH As As As As As needed needed needed needed needed Plating conditions pH 9.5 9.5 9.5 9.5 9.5 Bath temperature 70° C. 70° C. 70° C. 70° C. 70° C. (° C.) Deposition rate (μm/h) 9.2 2 8.9 5.5 4 Bath stability ⊚ ⊚ ⊚ ⊚ ⊚

Table 7 shows that the electroless Ni—Fe alloy plating solutions in which the contents of the nickel ion source and the ferric ion source are 0.06 mol/L, respectively, the content of the first complexing agent is 0.05 to 0.15 mol/L, and the content of the second complexing agent is 0.3 mol/L provide excellent bath stability. The table also shows that the electroless Ni-Fe alloy plating solutions in which the contents of the nickel ion source and the ferric ion source are 0.06 mol/L, respectively, the content of the first complexing agent is 0.1 mol/L, and the content of the second complexing agent is 0.1 to 0.4 mol/L provide excellent bath stability. This suggests that continuous plating can be performed in a stable manner with the electroless Ni—Fe alloy plating solutions of Examples 6a to 6e.

7. Evaluation of Concentration of Reducing Agent

First, the electroless Ni—Fe alloy plating solutions of Examples 7a and 7b shown in Table 8 were prepared in the same manner as in Example 3a. The electroless Ni—Fe alloy plating solutions of Examples 7a and 7b are the same except that the concentration of the reducing agent, i.e., sodium hypophosphite is different.

Then the composition of the coating prepared using the electroless Ni—Fe alloy plating solution of Examples 7a and 7b was analyzed in the same manner as in Example 3a, and as a result, the content of Ni was 65 to 95% by mass, the content of Fe was 1 to 35% by mass and the content of P was 0.1 to 7% by mass in all cases. Furthermore, the deposition rate was calculated and bath stability was evaluated in the same manner as in Example 3a. The results are shown in Table 8.

TABLE 8 Ex. 7a Ex. 7b Component Nickel ion NiSO₄ (mol/L) 0.06 0.06 constituting source plating bath Ferric ion Fe₂ (SO₄)₃ 0.06 0.06 source (mol/L) First Alanine (mol/L) 0.1 0.1 complexing agent Second Sodium 0.3 0.3 complexing tartrate agent (mol/L) Reducing Sodium 0.2 0.3 agent hypophosphite (mol/L) pH buffer Sodium 0.05 0.05 tetraborate (mol/L) Stabilizer 2-propyn-1-ol 10 10 (ppm) pH adjuster NaOH As As needed needed Plating conditions pH 9.5 9.5 Bath temperature 70° C. 70° C. (° C.) Deposition rate (μm/h) 3.5 2 Bath stability ⊚ ⊚

Table 8 shows that the electroless Ni—Fe alloy plating solutions in which the content of sodium hypophosphite is 0.2 to 0.3 mol/L provide excellent bath stability. This suggests that continuous plating can be performed in a stable manner with the electroless Ni—Fe alloy plating solutions of Examples 7a and 7b.

8. Evaluation of Type of Stabilizer

First, the electroless Ni—Fe alloy plating solutions of Examples 8a to 8i shown in Table 9 were prepared in the same manner as in Example 3a. The electroless Ni—Fe alloy plating solution of Example 8a does not contain stabilizer. The electroless Ni—Fe alloy plating solutions of Examples 8b to 8i are the same except for using any one of bismuth, lead, antimony, vanadium, thiourea, sodium thiocyanate, sodium nitrobenzenesulfonate and 2-propyn-1-ol as a stabilizer.

Then the composition of the coating prepared using the electroless Ni—Fe alloy plating solution of Examples 8a to 8i was analyzed in the same manner as in Example 3a, and as a result, the content of Ni was 65 to 95% by mass, the content of Fe was 1 to 35% by mass and the content of P was 0.1 to 7% by mass in all cases. Furthermore, the deposition rate was calculated and bath stability was evaluated in the same manner as in Example 3a. The results are shown in Table 9.

TABLE 9 Ex. 8a Ex. 8b Ex. 8c Ex. 8d Ex. 8e Ex. 8f Ex. 8g Ex. 8h Ex. 8i Component Nickel ion NiSO₄ (mol/L) 0.06 0.06 0.06 0.06 0.06 0.06 0.06 0.06 0.06 constituting source plating bath Ferric ion Fe₂ (SO₄)₃ 0.01 0.01 0.01 0.01 0.01 0.01 0.01 0.01 0.01 source (mol/L) First Alanine (mol/L) 0.1 0.1 0.1 0.1 0.1 0.1 0.1 0.1 0.1 complexing agent Second Rochelle salt 0.3 0.3 0.3 0.3 0.3 0.3 0.3 0.3 0.3 complexing (mol/L) agent Reducing Sodium 0.15 0.15 0.15 0.15 0.15 0.15 0.15 0.15 0.15 agent hypophosphite (mol/L) pH buffer Sodium 0.05 0.05 0.05 0.05 0.05 0.05 0.05 0.05 0.05 tetraborate (mol/L) Stabilizer Bismuth (ppm) — 0.5 — — — — — — — Lead (ppm) — — 0.5 — — — — — — Antimony (ppm) — — — 10 — — — — — Vanadium (ppm) — — — — 10 — — — — Thiourea (ppm) — — — — — 0.5 — — — Sodium — — — — — — 10 — — thiocyanate (ppm) Sodium — — — — — — — 10 — nitrobenzene- sulfonate (ppm) 2-propyn-1-ol — — — — — — — — 10 (ppm) pH adjuster NaOH As As As As As As As As As needed needed needed needed needed needed needed needed needed Plating conditions pH 9.5 9.5 9.5 9.5 9.5 9.5 9.5 9.5 9.5 Bath temperature 70° C. 70° C. 70° C. 70° C. 70° C. 70° C. 70° C. 70° C. 70° C. (° C.) Deposition rate (μm/h) 6.9 6.7 6.5 6.4 6.4 6.8 6.8 6.9 6.3 Bath stability ◯ ◯ ◯ ⊚ ◯ ⊚ ⊚ ◯ ⊚

Table 9 shows that although the electroless Ni—Fe alloy plating solution substantially provides good bath stability even without a stabilizer (see Example 8a), using a stabilizer improves bath stability. The table also shows that antimony, thiourea, sodium thiocyanate and 2-propyn-1-ol are particularly preferred as a stabilizer. This suggests that continuous plating can be performed in a more stable manner with the electroless Ni—Fe alloy plating solutions of Examples 8b to 8i.

9. Evaluation of pH

First, the electroless Ni—Fe alloy plating solutions of Examples 9a to 9f shown in Table 10 were prepared in the same manner as in Example 3a. The electroless Ni—Fe alloy plating solutions of Examples 9a to 9f are the same except that the pH is different.

Then the composition of the coating prepared using the electroless Ni—Fe alloy plating solution of Examples 9a to 9f was analyzed in the same manner as in Example 3a, and as a result, the content of Ni was 65 to 95% by mass, the content of Fe was 1 to 35% by mass and the content of P was 0.1 to 7% by mass in all cases. Furthermore, the deposition rate was calculated and bath stability was evaluated in the same manner as in Example 3a. The results are shown in Table 10.

TABLE 10 Ex. 9a Ex. 9b Ex. 9c Ex. 9d Ex. 9e Ex. 9f Component Nickel ion NiSO₄ (mol/L) 0.06 0.06 0.06 0.06 0.06 0.06 constituting source plating bath Ferric ion Fe₂ (SO₄)₃ 0.01 0.01 0.01 0.01 0.01 0.01 source (mol/L) First Alanine (mol/L) 0.1 0.1 0.1 0.1 0.1 0.1 complexing agent Second Sodium 0.3 0.3 0.3 0.3 0.3 0.3 complexing tartrate agent (mol/L) Reducing Sodium 0.15 0.15 0.15 0.15 0.15 0.15 agent hypophosphite (mol/L) pH buffer Sodium 0.05 0.05 0.05 0.05 0.05 0.05 tetraborate (mol/L) Stabilizer 2-propyn-1-ol 10 10 10 10 10 10 (ppm) pH adjuster NaOH As As As As As As needed needed needed needed needed needed Plating conditions pH 9 9.3 9.5 9.7 10 11 Bath temperature 70° C. 70° C. 70° C. 70° C. 70° C. 70° C. (° C.) Deposition rate (μm/h) 4.22 5.3 6.3 5.7 5.5 5.4 Bath stability ⊚ ⊚ ⊚ ⊚ ⊚ ⊚

Table 10 shows that the electroless Ni—Fe alloy plating solutions having a pH of 9 to 11 provide excellent bath stability. This suggests that continuous plating can be performed in a stable manner with the electroless Ni—Fe alloy plating solutions of Examples 9 to 9f.

10. Evaluation of Bath Temperature

First, the electroless Ni—Fe alloy plating solutions of Examples 10a to 10f shown in Table 11 were prepared in the same manner as in Example 3a, and plating operation was carried out in the same manner as in the case where the electroless Ni—Fe alloy plating solution of Example 2a was used. The composition of the bath of the electroless Ni—Fe alloy plating solutions of Examples 10a to 10f is the same, and the bath temperature is different.

Then the composition of the coating prepared using the electroless Ni—Fe alloy plating solution of Examples 10a to 10f was analyzed in the same manner as in Example 3a, and as a result, the content of Ni was 65 to 95% by mass, the content of Fe was 1 to 35% by mass and the content of P was 0.1 to 7% by mass in all cases. Furthermore, the deposition rate was calculated and bath stability was evaluated in the same manner as in Example 3a. The results are shown in Table 11.

TABLE 11 Ex. 10a Ex. 10b Ex. 10c Ex. 10d Component Nickel ion NiSO₄ (mol/L) 0.06 0.06 0.06 0.06 constituting source plating bath Ferric ion Fe₂ (SO₄)₃ 0.06 0.06 0.06 0.06 source (mol/L) First Alanine (mol/L) 0.1 0.1 0.1 0.1 complexing agent Second Sodium 0.3 0.3 0.3 0.3 complexing tartrate agent (mol/L) Reducing Sodium 0.15 0.15 0.15 0.15 agent hypophosphite (mol/L) pH buffer Sodium 0.05 0.05 0.05 0.05 tetraborate (mol/L) Stabilizer 2-propyn-1-ol 10 10 10 10 (ppm) pH adjuster NaOH As As As As needed needed needed needed Plating conditions pH 9.5 9.5 9.5 9.5 Bath temperature 60 70 75 80 (° C.) Deposition rate (μm/h) 1.8 6.3 11.3 14.8 Bath stability ⊚ ⊚ ⊚ ⊚

Table 11 shows that the electroless Ni—Fe alloy plating solutions provide excellent bath stability at a bath temperature of 60 to 80° C. This suggests that continuous plating can be performed in a stable manner with the electroless Ni—Fe alloy plating solutions of Examples 10a to 10d.

11. Evaluation of Electroless Ni—Fe Alloy Plating Solution having Other Composition

In the following, electroless Ni—Fe alloy plating solutions having a composition different from that of the electroless Ni—Fe alloy plating solutions described above will be evaluated. First, the electroless Ni—Fe alloy plating solutions of Examples 11a to 11d shown in Table 12 and the electroless Ni—Fe alloy plating solutions of Examples 12a to 12e shown in Table 13 were prepared. The electroless Ni—Fe alloy plating solutions of Examples 11d contains three complexing agents, and ammonium sulfate mainly acts as the first complexing agent, and Rochelle salt and trisodium citrate mainly act as the second complexing agent. Then the composition of the coating prepared using the electroless Ni—Fe alloy plating solution of Examples 11a to 11d and 12a to 12e was analyzed, the deposition rate was calculated and bath stability was evaluated in the same manner as in Example 3a. The results are shown in Table 12 and Table 13.

TABLE 12 Ex. 11a Ex. 11b Ex. 11c Ex. 11d Component Nickel ion NiCl₂ (mol/L) 0.06 0.06 0.06 0.06 constituting source plating bath Ferric ion Fe₂ (SO₄)₃ 0.01 0.01 0.01 0.01 source (mol/L) First Ammonium 0.25 0.5 0.75 0.25 complexing sulfate agent (mol/L) Second Rochelle salt 0.23 0.23 0.23 0.23 complexing (mol/L) agent Trisodium — — — 0.1 citrate (mol/L) Reducing Sodium 0.13 0.13 0.13 0.13 agent hypophosphite (mol/L) Stabilizer Bismuth (ppm) 0.5 0.5 0.5 0.5 pH adjuster NaOH As As As As needed needed needed needed Plating conditions pH 10.5 10.5 10.5 10.5 Bath temperature 70 70 70 70 (° C.) Deposition rate (μm/h) 11 11 8.9 8.5 Composition of Content of Ni 84.7 81.6 80.1 83.6 coating (wt %) Content of Fe 14.9 18.3 19.7 16.1 (wt %) Content of P 0.3 0.1 0.3 0.3 (wt %) Bath stability ⊚ ⊚ ⊚ ⊚

TABLE 13 Ex. 12a Ex. 12b Ex. 12c Ex. 12d Ex. 12e Component Nickel ion NiSO₄ (mol/L) 0.3 0.3 0.3 0.3 0.3 constituting source plating bath Ferric ion Fez (SO₄)₃ 0.02 0.02 0.02 0.02 0.02 source (mol/L) First Ammonium 0.1 0.2 0.4 0.2 0.2 complexing sulfate agent (mol/L) Second Trisodium 0.1 0.1 0.1 0.1 0.1 complexing citrate agent (mol/L) Reducing Dimethylamine- 0.05 0.05 0.05 0.05 0.05 agent borane (mol/L) Stabilizer Bismuth (ppm) 0.5 0.5 0.5 0.5 0.5 pH adjuster NaOH As As As As As needed needed needed needed needed Plating conditions pH 9 9 9 8.5 9.5 Bath temperature 80 80 80 80 80 (° C.) Deposition rate (μm/h) 1.4 2.8 2.3 0.9 4.6 Composition of Content of Ni 70.4 75.8 81.2 66.2 74.5 coating (wt %) Content of Fe 29.6 24.2 18.3 33.8 25.5 (wt %) Bath stability ⊚ ⊚ ⊚ ⊚ ⊚

As shown in Table 12 and Table 13, since the electroless Ni—Fe alloy plating solutions of Examples 11a to 11d and 12a to 12e have excellent bath stability, continuous plating can be performed in a stable manner.

Industrial Applicability

The electroless Ni—Fe alloy plating solution containing a nickel ion source and a ferric ion source of the present invention enables continuous plating to be performed in a stable manner, and thus productivity can be improved and production cost can be decreased. The electroless Ni—Fe alloy plating solution can be applied to various technical fields in which a conventional electroless Ni—Fe alloy plating solution containing a nickel ion source and a ferrous ion source is used, such as production of magnetic field shielding materials, magnetic heads and wound magnetic cores. 

1. An electroless Ni—Fe alloy plating solution, comprising a nickel ion source, an iron ion source, a complexing agent and a reducing agent, wherein the iron ion source is a ferric ion source.
 2. The electroless Ni—Fe alloy plating solution according to claim 1, wherein the ferric ion source is one or two or more iron salts selected from the group consisting of iron (III) sulfate, iron (III) chloride, iron alum, iron (III) oxide and iron (III) hydroxide.
 3. The electroless Ni—Fe alloy plating solution according to claim 1, wherein the content of the ferric ion in the electroless Ni—Fe alloy plating solution is 0.001 to 1.0 mol/L at the time of initial make-up of plating bath.
 4. The electroless Ni—Fe alloy plating solution according to claim 1, wherein the content of the ferrous ion at the electroless Ni—Fe alloy plating solution is 0.1 mol/L or less at the time of initial make-up of plating bath.
 5. The electroless Ni—Fe alloy plating solution according to claim 1, wherein the nickel ion source is one or two or more nickel salts selected from the group consisting of nickel chloride, nickel sulfate, nickel sulfamate, nickel hypophosphite, nickel citrate, nickel carbonate and nickel acetate.
 6. The electroless Ni—Fe alloy plating solution according to claim 1, wherein the complexing agent is one or two or more complexing agents selected from the group consisting of tartaric acid, citric acid, gluconic acid, pyrophosphoric acid, etidronic acid, alanine, glycine, glutamic acid, hydantoin, arginine, acetic acid, succinic acid, ascorbic acid, butyric acid, fumaric acid, pyruvic acid, lactic acid, malic acid, oxalic acid, ammonia, monoethanolamine, triethylenetetramine, triethanolamine, ethylenediamine, ethylenediaminetetraacetic acid and a salt thereof.
 7. The electroless Ni—Fe alloy plating solution according to claim 1, wherein the reducing agent is one or two or more reducing agents selected from the group consisting of hypophosphorous acid, hypophosphite, dimethylamineborane, titanium (III) and hydrazine. 